Inverse reducer circuit



Aug. 10, 1937. J; GROSS 2,089,358

INYERSE REDUCER C IRGUIT Filed May 28, 1934 INVENTOR NALVERN u. ease B 0, I

TTOR Y Patented Aug. 10, 1937 PATENT OFFICE INVERSE REDUCER CIRCUIT Malvern J. Gross, Chicago, Ill., assignor to General Electric X-Ray Corporation, a corporation of New York Application May 28, 1934, Serial No. 727,953

3 Claims.

The present invention relates to a circuit for use with a unilaterally conductive device. The circuit illustrating the invention includes an X-ray tube as a load.

Separate rectification of alternating current has been generally abandoned for low energy X-ray tubes. Self rectifying tubes requiring low energy and without separate rectification have been satisfactory to a fair degree. Circuits without separate rectification develop an inverse voltage larger than the useful voltage. This has made it necessary to design such X-ray and other apparatus for voltages in excess of those actually employed. This has limited the expansion of self rectifying devices to larger voltages. It has been usual to make apparatus employing self rectifying X-ray tubes with a margin of safety in insulation and otherwise approximating tWenty-five per cent of the normal operating voltage. An X-ray apparatus designed to use sixty kilovolts and of conventional design usually is built to handle with safety at least eighty kilovolts because of the presence of inverse energy. Various devices and circuits have been proposed for overcoming the difiiculties incident to the development of such inverse energy. These devices and circuits may be designated as inverse suppressors.

One of the circuits for suppressing inverse is illustrated and described in the patent to William K. Kearsley, Number 1,890,330, issued December 6, 1932, and entitled Apparatus for and method of operating rectifying load devices. Such Kearsley inverse suppressor operates with all types of transformers. Transformers of given characteristics, however, appear to possess better inverse suppressing capabilities than other transformers when used with the Kearsley circuit. Ithas been demonstrated by experiment in respect to certain transformers that if a limited proportion of exciting current is supplied to the primary of the transformer during the inverse half-Wave, the inverse suppressing characteristics of the circuit are improved. The exciting current supplied during the inverse half-wave may be supplied in a number of different ways.

It may be supplied among others by the introduction of a leakage resistance across the rectifier in series with the primary of the high tension transformer; by a condenser placed in parallel with either the primary or the secondary of the high tension transformer or both, or by such condensers in conjunction with a leakage resistance across the rectifier in series with the primary of the high tension transformer.

The primary object of the present invention, therefore, is to increase the inverse suppressing capacity of a circuit like that shown in the Kearsley patent. Other objects of-the invention include a new circuit or circuits having enlarged inverse suppressing values.

These objects, and such other objects as may hereinafter appear, are obtained by the novel arrangement, unique combination, and improved construction of the several elements constituting the circuit illustrated in the accompanying single sheet of drawing in which the figure is a diagrammatic representation of an improved circuit forming the subject matter of the present invention. An X-ray tube is shown in said circuit as a unilaterally conductive load.

Like reference characters are used to designate similar parts in the drawing and in the following description of the new and improved circuit.

The circuit includes a high tension transformer having a magnetic core I I, a primary I2, and a secondary I3. Electrical energy is conducted by conduit I 4 from one terminal of the secondary I3 to the anode I8 of an X-ray tube I6. The anode I8 comprises a head having therein a refractory metal target 26 and a stem 2'! within the tube I6 for supporting said head. Stem 2'! at its external end is surrounded by fins 28 designated generally in the art as a radiator.

The other terminal of the secondary I3 is electrically connected by conduit I5 to a cathode structure 17. The cathode structure I! includes a focusing cup and a filament I9 Within the focusing cup. The filament I9 is energized by alternating current potential supplied by conduits 2I and 20 connected to opposite ends of a secondary 23 of a step-down transformer having a magnetic core 22. The primary of the stepdown transformer is designated 24.

Condenser 50 is connected across the terminals of the secondary I3.

Primary l2 and primary 24 of the high tension transformer and of the filament current transformer, respectively, are energized by current flowing from conduits or lines 36 and 31 in electrical connection with a source of alternating current potential (not shown). Conduits 34 and 35 are electrically connected to the lines 36 and 37 and the latter are connected to opposite terminals of the primary 24 of the step-down transformer.

A conduit 39 extends from the line 31 to one terminal of the primary I2. A conduit 38 extends from the other terminal of said primary I2 to a plate 3| in a valve 29. The valve is of a vacuum type and has a filament within the glass envelope thereof. A predetermined quantity of mercury 32 is sealed within such envelope.

The filament 30 in the valve 29 is energized by current flowing from the secondary of a stepdown transformer 33. The primary of the stepdown transformer 33 is electrically connected at its opposite terminals through conduits 34 and to the lines 3! and 36, respectively. One of primary With Kearsley inverse suppres- With Kearsley inverse suppresthe legs of the circuit between the secondary of said transformer 33 and the filament 30 has connected thereto a conduit 40 which is in electrical connection with aconduit 4!. having therein a manually controlled switch 42. The conduit 4! is in electrical connection with line 36.

A condenser 51 is connected across the con'" duits 38 and 39. A leakage resistance across the valve 29 in series with the primary l2 of the high tension transformer comprisesfconduits 53 and 54 having resistance 52 therein.

Alternating current potential is supplied by the lines 35 and 31. Such-potential energizes the primary of the filament current transformer to provide filament current in the valve 29 through the step-down transformer 33. The current flowing in lines 36 and 31 also energizes the primary l2 of the high tension transformer. The energization of the primary of said high tension transformer is acquired. from alternate half cycles of low tension current because of the valve 29 in circuit therewith.

Other devices may be substituted for those shown. Onecondenser may be employed, or two, or the resistance leakage employed without or with one or both of the condensers. The circuit may be modified .tomeet. special requirements. Any. of such devices 'or any combination thereof permits of the flow of magnetizing current of predetermined value in the high tension transformer during the inverse half wave.

The following tabulation was made as a result of experiments with an X-ray tube excited by a sixty milliampere current and having a constant inverse voltage of eighty-five kilovolts peak.

sor With Kearsley inverse suppressor and 25 microfarads across primary 60 85 5 With Kearsley inverse suppressor and 80 microfarads across primary. 60 83 2 With Kearsle 'nverse suppressor and 300 microfarads across sor and .002 microfarad across secondary 60 85 80 5 With Kearsley inverse suppressor and .004 microfarad across secondary 60 85 83 2 With Kearsley inverse suppress sor and 25 ohms resistance across valve 60 85 78 7 With Kearsley inverse suppressor and 50 ohms resistance across valve 60 85 81 4 With Kearsley inverse suppressor and ohms resistance across valve 60 85 83 2 sor and 200 ohms resistance 7 across valve 60 85 75 10 The Kearsley circuit, as shown by such experiments, has a definite inverse suppressing quality. This quality is enhanced by the modifications hereinabove described. It is established by the experiments which have been conducted that a certain minimum value of capacity across the primary and another certain minimum value of capacity across the secondary are necessary to. attain maximum inverse suppression. Resistance in parallel with the valve is critical in that a certain minimum value is necessary. Any large increase over such minimum value adversely affects the inverse suppressing qualities of such resistance.

What is claimed as new and is desired to be secured by Letters Patent of the United States 1. An X-ray system comprising a transformer having a primary winding and a secondary winding, an X-ray tube, a high tension circuit including the secondary winding ofsaid transformer, a source of alternating current potential, a low tension circuit including said source of potential and the primary winding of said transformer, a valve rectifier in said low tension circuit and in series with said primary winding, and a condenser in one of said circuits in parallel with one of the windings of said transformer for delivering an exciting current of predetermined value in said transformer during the inverse half wave. 7

2. An X-ray system comprising a transformer having a primary and a secondary, an Xray tube, a high tension circuit including the secondary of said transformer and said tube, a source of alternating current potential, a low tension circuit including said source of potential and the primary of said transformer, a valve rectifier in said low tension circuit, and resistance means in parallel with said valve rectifier for delivering an exciting current of predetermined value in said transformer during the inverse half wave.

3. An X-ray system comprising a transformer having a primary and a secondary, an X-ray tube, a high tension circuit including the secondary of said transformer and said tube, a source of alternating current potential, a low tension circuit including said source of potential and the primary of said transformer, a valve rectifier in said primary circuit, and a condenser in one of said circuits and a resistance in parallel with said valve rectifier for delivering an exciting current of predetermined Value in said transformer during the inverse half Wave. 

